Malaria vaccines is a hot research topic in Malaria World and is addressed this week in two highlighted news articles and three research papers.
One research paper is a review ‘Malaria Vaccines: Current Achievements and Path Forward’ by Chen et al. It summarises the current establishment views describing the two approved vaccines, RTS, S/AS01(Mosquirix by GlaxoSmithKline) and R21/Matrix-M (developed by Oxford University and the Serum Institute of India). It also introduces 13 other vaccines in development that are described as either Pre-erythrocytic stage, Blood stage or Sexual stage.
One of these, the Pre-erythrocytic PfSPZ vaccine is the subject of one of the news articles, ‘Sanaria reports positive initial safety results for groundbreaking PfSPZ-LARC2 malaria vaccine’. No details are included though the press release says physician-scientists at Groupe de Recherche Action en Santé (GRAS) in Burkina Faso have successfully completed initial safety evaluations in 30 adult Burkinabés as the first phase of a clinical trial of Sanaria® PfSPZ-LARC2 Vaccine, which is designed to prevent infection with Plasmodium falciparum malaria. The initial data of the 30 adults confirmed the vaccine was safe, fully attenuated, and caused no malaria infections. It does not say if a control was used or if there were any side effects.
One scientific paper is an animal study (‘Epitope specificity of antibody-mediated protection induced in mice by the malaria vaccine RTS,S/AS01’ by Flores-Garcia et al) and I will not consider it as it does not address real world efficacy.
The other two articles are not very positive of the effect of vaccines at combating malaria. One is a podcast, The Johns Hopkins Malaria Minute, ‘Why malaria vaccines may work better in some places than others (with Lemu Golassa)’. Professor Lemu Golassa, Head of Medical Parasitology at Addis Ababa University in Ethiopia stated that the RTS, S/AS01 and R21/Matrix-M are unsuitable for combatting he strains of Plasmodium falciparum circulating in Ethiopia.
The research paper ‘Efficacy of RTS,S/AS01E only seen in baseline parasitemic and not baseline aparasitemic Plasmodium falciparum-exposed, drug-treated Kenyan adults’ by Copeland et al found that the RTS,S/AS01 did not prevent malaria in Kenyan adults who did not have the parasite prior to vaccination. There was a modest benefit in preventing malaria in those already infected. However, the control groups in this study received intramuscular injection with a rabies vaccine (Abhayrab®, Human Biologicals Institute, Andra Pradesh, India). This questionable practice was addressed in my first blog post ‘R21 Vaccine is less toxic and ineffective than a Rabies Vaccine’.
Indeed, in this study for the subjects with negative PCRs for malaria parasites, while not statistically significant (-24%, 95% CI; -97 to 22.4; p=0.373) the unadjusted estimated vaccine efficacy is lower for Mosquirix® than for Abhayrab®. The Bill and Melinda Gates Foundation funded study concludes that a vaccine comprising only the CS (circumsporozoite) protein is unlikely to be sufficient to accelerate Pf malaria elimination due to modest efficacy in preventing infection, including in adults. It calls for more research on multi-antigen/multi-stage vaccine approaches that include a CS-component, as well as a one or more blood-stage and/or sexual-stage (transmission-blocking) antigens.